An immunological method, free of non-specific effects, has been developed for the bulk yield of mRNA for individual globin-chain mRNA from reticulocyte polysomes. Rabbit alpha mRNA thus isolated behaves electrophoretically as expected. mRNA from several species is to be used for assay of nucleotide distances between structural genes. Radiolabelled, reiterated DNA sequences specific for the human Y chromosome have been purified to the point where there is no cross-reaction with DNA from normal females. Relationship of these sequences to maleness is being defined via analysis of Y-chromosome variants with varying expression of male differentiation. BIBLIOGRAPHIC REFERENCES: Boyer, S.H., Smith, K.D., Noyes, A.N., and Mullen, M.A. Immunological characterization of rabbit hemoglobin alpha and beta chain-synthesizing polysomes. J. Biol. Chem. 249: 7210-7219, 1974. Smith, K.D., Kunkel, L., and Boyer, S. H. Isolation and uses of chromosome-specific reiterated DNA. In human Gene Mapping, 1975, Daniel Bergsma, Ed. Birth Defects: Original Article Series, The National Foundation. In press.